Add and subtract large numbers (5th grade math)
In this lesson, we add and subtract large numbers (with up to 9 digits, or with billions), both using mental math and in columns (one number under the other). The main principle to keep in mind is that the different places in the number need to be aligned: ones with ones, tens with tens, hundreds with hundreds, etc. all the way to hundred billions. Other than that, there's not really anything new to learn: the basic addition and subtraction algorithms (including regrouping) work the same way as with smaller numbers.
See also
The connection between multiplication and division, simple equations, bar models, terminology
More problem solving with bar models, part 1
Math Mammoth Grade 5 curriculum